Camshaft adjustment is used on the intake side and/or exhaust side of an internal combustion engine to influences valve timing. The variation in valve timing is one approach to reduce fuel consumption, to reduce emissions, and/or to increase power.
On account of the limited resources of fossil fuels, there is a desire to minimize fuel consumption of internal combustion engines. Statutory regulations demand a constant reduction of pollutants emitted into the environment by internal combustion engines.
Fuel consumption and therefore efficiency present problems, particularly in spark ignition engines. The reason for this is the basic operating method of the spark ignition engine. The spark ignition engine operates with a homogeneous fuel/air mixture. The desired power is set by varying the filling of the combustion space, so that, in contrast to the diesel engine, the operating method of the spark ignition engine is based on quantity regulation.
Load control takes place by a throttle valve provided in the intake duct. By adjusting the throttle valve, the pressure of the intake air downstream of the throttle valve is affected. Quantity regulation by a throttle valve has thermodynamic disadvantages due to lower pressure and the associated throttle losses.
One approach to partially overcome throttling losses is to use a variable cam timing (VCT) drive. In conventional valve drives both the stroke of the valves and the opening and closing times of the intake and exhaust valves are invariable. But, with VCT, the valve opening and closing times can be altered so that a desired amount of air is inducted with a lesser need to throttle.
However, detectable fuel savings and therefore detectable pollutant reductions can also be achieved by only partially variable valve drives in which, for example, the closing time of the intake valve is adjusted. This measure—variation in the closing time of the intake valve—is likewise suitable for influencing the power or the torque of the internal combustion engine.
Moreover, in the case of a fully variable valve control, the quantity of the intake mixture can be controlled by the closing of the intake valve, the intake mixture being sucked in at ambient pressure, even in the case of a change of charge, in the part load range because of the absence of a throttle valve.
One possibility of varying the control times of the valves is to use VCT, by which the camshaft is rotated with respect to the crankshaft to advance or retard the valve events with respect to the crankshaft. Such VCT devices are designated below, in general, as camshaft adjusters, irrespective of the operating principle on which they are based.
VCTs are normally actuated or controlled hydraulically, one or more pressure chambers being acted upon by hydraulic oil in a directed manner. Such an adjustment device is described, for example, in the German laid-open publication DE 198 50 947 A1. The camshaft adjuster described in DE 198 50 947 A1 is equipped with an axially displaceable piston device, an axial displacement of the piston device implying a rotation of the camshaft with respect to a belt wheel driving the camshaft and, consequently, a rotation of the camshaft with respect to the crankshaft which is coupled in its rotational movement to the belt wheel via a belt.
To displace the piston device, two adjustment chambers are provided, which are acted upon with pressure oil for axial displacement.
The adjustment device described is merely one example of a camshaft adjuster which is formed by an axially displaceable piston device.
U.S. Pat. No. 4,858,572 describes an adjustment device which does not make use, like the device described above, of a piston device to rotate the camshaft with respect to the crankshaft. Instead, a vane-cell pump is employed for adjustment. One or more chambers is supplied with a fluid under pressure, and therefore like the adjustment device in DE 198 50 947 A1, is based on a hydraulic operating method.
A vane-cell pump 100 has an outer rotor 102 and an inner rotor 104 and as shown in FIG. 1. The outer rotor 102 rotates with external belt gearwheel 101; whereas, the inner rotor 104 is fixed to the camshaft 103. To rotate camshaft 103 with respect to the crankshaft and consequently vary valve timing, inner rotor 104 is rotated with respect to outer rotor 102, by introducting fluid into pressure chambers 105. The pressure chambers 105 are formed by the vanes 102a, 104a of the rotors 102, 104 and by the rotors 102, 104 themselves and are sealed off by sealing strips arranged at the ends of the vanes 102a, 104a. By providing pressurized oil into the pressure chambers 105, the inner rotor 104 rotates with respect to the outer rotor 102.
Both the intake camshaft and the exhaust camshaft may be equipped in each case with a separate camshaft adjuster. However, depending on the objective, it may also be expedient to provide only one adjustable camshaft, e.g., only the intake camshaft or the exhaust camshaft, the other camshaft having fixed valve timings.
If, for example, the aim is to achieve fuel savings, varying the intake camshaft only may prove to be sufficient, without a VCT device on the exhaust camshaft.
In other applications, the opposite procedure may seem appropriate, in which the exhaust camshaft is equipped with a camshaft adjuster, whereas there are fixed intake valve events.
Providing the various options leads to considerable problems during assembly since the existing production lines have one assembly line to assemble all variations: VCT on both intake and exhaust, VCT on one of intake or exhaust, and no VCT.
Where assembly is concerned, the rotary angle positions of the camshafts and of the crankshaft are set and synchronized, inter alia, in a special production station. The crankshaft is rotated until it butts against a predetermined positioning pin, the camshafts being capable of being positioned and synchronized in that they are rotated into the corresponding rotary angle position by notches provided at their free shaft ends. An engagement of a tool into the gearwheels arranged on the camshafts, if appropriate with the subsequent rotation of the corresponding camshaft, ensures the synchronization of the gearwheels.
If the camshafts are equipped with camshaft adjusters, the synchronization of the two camshaft adjusters, together with the gearwheels, typically takes place by a positioning tool which engages in position marks provided on the two camshaft adjusters, in such a way that the positioning tool can engage into the position marks in only a single predeterminable arrangement of the two camshaft adjusters in relation to one another.
After the positioning and synchronization of the camshafts and crankshaft have taken place successfully, the gearwheels or the camshaft adjusters are fixed by screws to fasten a gearwheel or a camshaft adjuster to the camshaft, a screw being screwed in the direction of the longitudinal axis of the camshaft. In this case, during assembly, a screw is screwed into the intake camshaft and a screw is screwed into the exhaust camshaft.
As regards the assembly situation where both camshafts are equipped with a camshaft adjuster or else neither camshaft has such a camshaft adjuster, the tools for the production station have the same engagement depth for screwing in the screws.
In internal combustion engines in which a camshaft adjuster for implementing variable control times is provided only on the exhaust side or only on the intake side and only a gearwheel is arranged on the other camshaft, the engagement depth of the tools for installing the fasteners is different, due to the depth of the camshaft adjuster being installed in one case and not in the other.
The production stations used at the present time for assembly often have only the possibility of assembling internal combustion engines in which the penetration depth of the tools for installing the fasteners is identical.
The provision of an internal combustion engine in which only the intake camshaft or only the exhaust camshaft is equipped with a camshaft adjuster would therefore necessitate an additional production station, the tools of which have the possibility of operating at different penetration depths. However, this measure would lead to considerable investment costs, specifically not only in terms of the procurement costs of an additional production station, but also in terms of the area or space requirement which would be necessary for setting up this additional production station and consequently for extending the existing production line.
The inventors of the present invention have recognized that the manufacture of assembly of an internal combustion engine would be simpler and less costly if the penetration depth for installing the gearwheel fasteners were a consistent depth regardless of whether it is a variable camshaft or a fixed camshaft.